A 6.8 sigma anomaly in the invariant mass distribution of e+e- pairs produced via internal pair creation in 8Be nuclear transitions has been reported recently by Krasznahorkay et al. in Phys. Rev. Lett. 116 (2016) 042501. The data can be explained by a 17 MeV vector gauge boson X produced in the transition of an excited beryllium state to the ground state, 8Be* -> 8Be X, followed by the decay X -> e+e-. We find that the gauge boson X can be associated with a new protophobic fifth force (i.e. with a coupling to protons suppressed compared to its coupling to neutrons) with a characteristic range of 10 fm and milli-charged couplings to first generation quarks and electrons. We show that such a protophobic gauge boson is consistent with all available experimental constraints and we discuss several ways to embed this new particle into an anomaly-free extension of the Standard Model. One of the most appealing theories of this type is a model with gauged baryon number, in which the new gauge boson kinetically mixes with the photon, and provides a portal to the dark matter sector.